Other forces have also contributed to the formation of the Grand Canyon. Rainfall, melting snow and small tributary streams have all changed the landscape over time. The Grand Canyon developed its shape because the different layers of rock and soil erode at different rates and in various ways. Some types of rock erode into cliffs, while others form more gentle slopes. Since the Colorado River is still flowing and the area continues to receive rainfall and other weather events, the Grand Canyon's appearance continues to erode and change.